Microwave and rf ablation system and related method for dynamic impedance matching

ABSTRACT

An electrosurgical system and method for performing electrosurgery is disclosed. The electrosurgical system includes an electrosurgical generator adapted to supply electrosurgical energy to tissue. The electrosurgical system includes an electrosurgical instrument, such as an electrosurgical antenna, knife, forceps, suction coagulator, or vessel sealer. The disclosed system includes an impedance sensor, a controller, dynamic impedance matching network, and an electrosurgical energy generator. The dynamic impedance matching network includes a PIN diode switching array configured to selectively activate a plurality of reactive elements. The disclosed arrangement of reactive elements provides real-time impedance correction over a wide range of impedance mismatch conditions.

BACKGROUND

1. Technical Field

The present invention relates to systems and methods for performing amedical procedure, wherein the medical procedure includes transferringenergy from an energy source to a patient via a transmission line and,more particularly, dynamically matching energy source impedance totissue impedance.

2. Background of Related Art

Historically, surgery was performed using only mechanical tools, such asmechanical cutting instruments, scalpels, bladed forceps, saws,rongeurs, and the like. However, in recent years, technology hasimproved such that surgeons now frequently use electromagnetic waves torender a wider variety of surgical effects, e.g., by selectivelymodifying tissue using electromagnetic energy to produce a specificeffect. The characteristics of the electromagnetic energy applied totissue strongly correlates to the effect that the energy has on thetissue. These characteristics are therefore changed in accordance withthe desired tissue effect. Two types of electromagnetic energy that arecommonly applied during surgery include radiofrequency (RF)electrosurgical energy and microwave electrosurgical energy. During mostmedical procedures in which an energy source is employed, the energygenerated for the medical procedure is transferred to a patient via atransmission line. One example of a medical procedure employing anenergy source is an RF or microwave ablation surgical procedure. In anablation surgical procedure the energy generated may be an RF ormicrowave surgical signal having a frequency and a wavelength associatedtherewith.

During the ablation surgical procedure, the surgical signal may betransmitted to the patient via a transmission line. Generally, thetransmission line employed may have losses associated therewith that maybe attributable to many factors. Factors that can cause transmissionline losses include at least the following: the type of material usedfor the transmission line, the length of the transmission line, thethickness of the transmission line, and impedance mismatch between thetransmission line and tissue load.

Generally, electrosurgery utilizes an electrosurgical generator, anactive electrode and a return electrode. The electrosurgical generatorgenerates electrosurgical energy typically above 100 kilohertz to avoidmuscle and/or nerve stimulation between the active and return electrodeswhen applied to tissue. During electrosurgery, current generated by theelectrosurgical generator is conducted through the patient's tissuedisposed between the two electrodes. The electrosurgical energy isreturned to the electrosurgical source via a return electrode padpositioned under a patient (i.e., a monopolar system configuration) or asmaller return electrode positionable in bodily contact with orimmediately adjacent to the surgical site (i.e., a bipolar systemconfiguration). The current causes the tissue to heat up as theelectromagnetic wave overcomes the tissue's impedance. Although manyother variables affect the total heating of the tissue, usually morecurrent density directly correlates to increased heating.

Microwave surgical procedures invoke the application of microwave energyto tissue. Unlike low frequency RF therapy that heats tissue withcurrent, microwave therapy heats tissue within the electromagnetic fielddelivered by an energy delivery device (e.g., a microwave antenna).Microwave surgical procedures typically utilize a microwave generatorand an energy delivery device that delivers the microwave energy to thetarget tissue. One type of energy delivery device is a coaxial microwaveantenna that forms an approximate dipole antenna. Microwave surgicalsystems involve applying microwave radiation to heat, ablate and/orcoagulate tissue. For example, treatment of certain diseases requiresdestruction of malignant tissue growths (e.g., tumors) or surroundingtissue. It is known that tumor cells denature at elevated temperaturesthat are slightly lower than temperatures injurious to surroundinghealthy cells. Therefore, by applying microwave energy to heat tumorcells to temperatures above 41° C. kills the tumor cells while adjacenthealthy cells are maintained at lower temperatures avoiding irreversiblecell damage. Another method used to treat diseased tissue is to resect aportion of the diseased organ, tissue or anatomical structure. Forexample, a liver may contain diseased tissue and healthy tissue. Onetreatment option is to pre-coagulate and ablate some of the liver tissueto facilitate resection of a portion of the liver including the diseasedtissue. Microwave energy can be used during these types of procedures topre-coagulate tissue prior to resection, to reduce bleeding duringresection and to facilitate the actual resection of the tissue.

The microwave energy may be applied via an antenna that can penetratetissue. There are several types of microwave antennas, such as monopoleand dipole antennas. In monopole and dipole antennas, most of themicrowave energy radiates perpendicularly away from the axis of theconductor. A monopole antenna includes a single, elongated conductorthat transmits the microwave energy. A typical dipole antenna has twoelongated conductors parallel to each other and positioned end-to-endrelative to one another with an insulator placed therebetween. Each ofthe conductors is typically about ¼ of the length of the wavelength ofthe microwave energy making the aggregate length of both conductorsabout ½ of the wavelength of the microwave energy. Additionally, amicrowave antenna may be adapted for use in a specific manner, forexample, for endoscopic or laparoscopic (minimally invasive) procedures,for open procedures, and for percutaneous procedures.

It is known in the art that in order to maximize the amount of energytransferred from the source (microwave or RF generator) to the load(surgical implement or tissue), the line and load impedances shouldmatch. If the line and load impedances do not match (i.e. impedancemismatch) a reflected wave may be created. The ratio of the forward(primary) wave amplitude to the reflected wave amplitude is expressed asa reflection coefficient Γ. Standing waves within the transmission linemay result from constructive and destructive interference betweenforward and reflected waves. The ratio between the wave maxima resultingfrom constructive interference and minima resulting from destructiveinterference is referred to as the voltage standing wave ratio, or VSWR.As an example, an unbalanced transmission line may exhibit anundesirably large VSWR up to around 4:1.

Standing waves created within the transmission line can contribute tothe power loss associated with impedance mismatch, cause inaccurateenergy dose (i.e., power) measurements, and impair monitoring ofparameters associated with the surgical procedure. Moreover, standingwaves may cause localized heating and failure of an interconnect (i.e.,cable or coaxial cable), and cause premature wear and/or failure of themicrowave or RF generator.

Further, during a typical ablation surgical procedure, the impedance atthe surgical site changes over the course of the ablation procedure.This is because of tissue necrosis associated with the ablation surgicalprocedure. Generally, the energy source may include an impedancematching circuit and/or tuner, which may be configured to compensate forimpedance changes at the surgical site.

Conventional impedance matching circuits may include devices such asmotor-driven variable reactive elements, i.e., vacuum variablecapacitors, and as a result may be large in size. In addition, becausethe energy source may have a much smaller wavelength than the length ofthe transmission line, it is often difficult to achieve accurateimpedance matching in a rugged, reliable, and relatively compact design.

SUMMARY

A system and method for impedance matching during an electrosurgicalmedical procedure is disclosed. The disclosed system may employ anenergy source, such as an electrosurgical generator, wherein the energysource may be connected to an energy delivering device via atransmission line. In one embodiment, the transmission line may be acoaxial cable. The disclosed system includes a dynamic impedancematching network having the capability to dynamically adjust to thevarying load conditions. In embodiments, the dynamic impedance matchingnetwork is adapted to automatically adjust, or “self-tune”, the energydelivery system to maintain a VSWR of less than about 1.5:1. It isenvisioned that disclosed dynamic impedance matching network may have arelatively compact size, for example, occupying a printed circuit board(PCB) of less than about 30 cm². It is to be understood, however, thatin embodiments, the disclosed dynamic impedance matching network mayoccupy a space less than, or greater than, about 30 cm². In embodiments,the PCB may be formed from any suitable material, for example withoutlimitation, aluminum oxide (Al₂O₃). In embodiments, the electrosurgicalgenerator is configured to generate an electrosurgical signal at afrequency in a range of about 915 mHz to about 925 mHz.

In one aspect of the present disclosure, a dynamic impedance matchingnetwork includes switchable reactive elements arranged in a piconfiguration having a first shunt reactive leg, a series reactive leg,and a second shunt reactive leg. In embodiments the first shunt reactiveleg includes a reactive element having a fixed value. The seriesreactive leg and the second shunt reactive leg each include a pluralityof reactive elements arranged in a switchable configuration, such thatthe individual reactive elements contained therein may be selectivelyactivated, separately or in combination, to achieve a desired (i.e.,selectively variable) leg reactance. In embodiments, the reactiveelements may include discrete components, such as without limitationsurface mount capacitors (i.e., “chip caps”), inductive coils, tunedstubs formed on the PCB, capacitors formed on the PCB, and/or inductorsformed on the PCB. In embodiments, a PCB capacitor may be formed by atleast two adjacently disposed PCB traces (i.e., foil traces). A PCBcapacitor constructed in this manner may be formed from traces disposedon the same side of the PCB or on traces formed on opposite side of thePCB. In embodiments, a PCB capacitor may have a dielectric portion thatincludes air and/or the PCB substrate.

An electrosurgical ablation system may be characterized by a range ofantenna-to-tissue impedance values (i.e., impedance mismatches). Thevalues of reactive elements in a dynamic impedance matching network ofthe present disclosure are selected accordingly to facilitate impedancematching over the range of mismatched values. Advantageously, theinventors have discovered that the identified range of mismatchedantenna-to-tissue impedances can be corrected, i.e., effectivelyimpedance matched, by the selective activation of four discrete valuesof series leg reactance and two discrete values of second shunt legreactance. By this arrangement, sixty-four overlapping reactance rangesare available to dynamically impedance match the antenna to tissue. Thatis, the sixty-four overlapping ranges define an aggregate range ofimpedance matching ability which corresponds to the identified range ofantenna-to-tissue impedance mismatch.

Each unique combination of reactive elements may be characterized by acircular region on a Smith diagram representing the reflectioncoefficient Γ of the unique combination combination. The position ofcenter point of the circular region on the Smith diagram is determinedby the aggregate value of the series leg reactance and represents a zeroreflection coefficient Γ for the unique combination (i.e., perfectimpedance matching). The diameter of the circular region represents theset of nominal reflection coefficient Γ values which fall within anacceptable tolerance of reflection coefficient Γ, that is, the circleencloses those nominal reflection coefficient Γ values which exhibitacceptable impedance matching. In embodiments, an acceptable reflectioncoefficient Γ is less than about 0.15, which has been determined tocorrespond to a power transfer efficiency (i.e., match efficiency) ofgreater than about 96%.

In another aspect of the present disclosure, a PIN diode switch array isprovided. The PIN diode array is configured to selectively activate atleast one of the reactive elements. The PIN diode array is furtherconfigured dynamically activate/deactivate reactive elements (“hotswitch”) during application of electrosurgical energy. The PIN diodeswitch array may additionally or alternatively include field-effecttransistor (FET) switching elements and/or microelectromechanical (MEMS)switching elements.

In yet another aspect, an electrosurgical system in accordance with thepresent disclosure includes a controller. The controller may beconfigured to receive any of a user input, an input related toimpedance, a phase input, and/or a temperature input. The controller mayfurther be configured to output any of a generator control signal, a PINdiode switch array control signal, and/or a user interface signal (i.e.,a visual, audible, or haptic indicator). In embodiments, the controllerincludes a processor. For example without limitation, the controller mayinclude a Cypress programmable system on a chip (PSOC), a PIC processor,a gate array or any suitable processor or chipset now or in the futureknown. The controller may be configured to execute a set of programmableinstructions embodying a method of dynamically matching impedance asdisclosed herein.

In still another aspect, an electrosurgical system in accordance withthe present disclosure includes an RF measurement module configured tosense impedance and phase angle (i.e., phase shift) within theelectrosurgical circuit. The RF Measurement module may include an AnalogDevice RFZ chip set configured to measure impedance and phase. The RFmeasurement module may be operatively coupled to at least one of theelectrosurgical generator, the dynamic impedance matching network,and/or the electrosurgical antenna or electrode. The RF measurementmodule may also be configured to be in communication with the controllermodule and/or to provide impedance signals to the controller.

Also disclosed is a method of performing an electrosurgical procedurethat includes the steps of providing an electrosurgical system thatincludes an electrosurgical instrument operatively coupled by atransmission line to an electrosurgical generator, a controller, animpedance sensor, a dynamic impedance matching network having includes aswitchable reactive elements arranged in a pi configuration thatincludes a first shunt reactive leg, a series reactive leg, and a secondshunt reactive leg, and a PINS diode array configured to selectivelyactivate the reactive elements; applying the electrosurgical instrumentto tissue; measuring the impedance of tissue; applying electrosurgicalenergy to tissue; and selectively activating at least one reactiveelement to match transmission line impedance to tissue impedance.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIG. 1A illustrates an exemplary impedance-matching electrosurgicalsystem according to the present disclosure operating in a monopolarmode;

FIG. 1B illustrates an exemplary impedance-matching electrosurgicalsystem according to the present disclosure operating in a bipolar mode;

FIG. 2 illustrates a block diagram of an embodiment of animpedance-matching electrosurgical system according to the presentdisclosure;

FIG. 3 is a circuit diagram of an embodiment of an dynamicimpedance-matching module in accordance with the present disclosure;

FIG. 4 is a Smith diagram illustrating relationships between reflectioncoefficient and impedance load;

FIGS. 5A-5J are Smith diagrams illustrating relationships betweenreflection coefficient, impedance load, and impedance correction.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail. Those skilled in the art will understand that thepresent disclosure may be adapted for use with either an endoscopicinstrument, laparoscopic instrument, or an open instrument. It shouldalso be appreciated that different electrical and mechanical connectionsand other considerations may apply to each particular type ofinstrument, however, the novel aspects with respect to electrosurgicalimpedance matching are generally consistent with respect to both theopen or endoscopic designs.

In the drawings and in the description which follows, the term“proximal” refers to the end of the instrument which is closer to theuser (i.e., further from the patient), while the term “distal” refers tothe end of the forceps which is further from the user (i.e., closer tothe patient).

With reference to FIG. 1A, there is shown an embodiment of animpedance-matching electrosurgical system 1 in a monopolar configurationin accordance with the present disclosure. An impedance-matchingelectrosurgical generation 10 is operably coupled to an electrosurgicalinstrument 15 by a transmission line 12. Transmission line 12 mayinclude a coaxial cable having a nominal impedance. In embodiments,transmission line 12 has a nominal impedance of about 50 ohms.Electrosurgical instrument 15 includes at least one electrode 16configured to deliver electrosurgical energy to an operative site ofpatient P, i.e., to tissue. Electrode 16 is in electrical communicationwith transmission line 12 and to impedance-matching electrosurgicalgenerator 10. Electrode 16 may be any suitable electrosurgicalelectrode, for example without limitation, a blade, a coagulator, aneedle, an antenna, or a snare. Impedance-matching electrosurgicalsystem 1 may additionally include an activation control (not explicitlyshown), such as without limitation a handswitch included in theelectrosurgical instrument 15 (not explicitly shown) or a footswitch(not explicitly shown). A return electrode 22 that is operably coupledto impedance-matching electrosurgical generator 10 by return conductor13 is affixed to patient P. In use, return electrode 22 provides areturn path for monopolar electrosurgical energy delivered by electrode16.

Turning to FIG. 1B, an embodiment of an impedance-matchingelectrosurgical system 1 in accordance with the present disclosure in abiopolar configuration is illustrated. An impedance-matchingelectrosurgical generator 10 is operably coupled to an electrosurgicalinstrument 18 by transmission lines 12, 14. In embodiments, transmissionlines 12, 145 may be included in a cable, i.e., a coaxial, twin-axial,and/or biaxial cable having a nominal impedance. In embodiments,transmission lines 12, 14 have a nominal impedance of about 50 ohms.Electrosurgical instrument 18 includes a bipolar electrode having twoelements 20, 21 configured to apply electrosurgical energy in a bipolarmode to an operative site of patient P, i.e., to tissue. Bipolarelectrode elements 20, 21 are in electrical communication withtransmission lines 12, 14, respectively, and to impedance-matchingelectrosurgical generator 10. Bipolar electrodes 20, 21 may be anysuitable electrosurgical electrode, for example without limitation,forceps, jaws, bypass cutters, anvil cutters, scissors, or a vesselsealer. Impedance-matching electrosurgical system 1 may additionallyinclude an activation control (not explicitly shown), such as withoutlimitation a handswitch included in the electrosurgical instrument 18(not explicitly shown) or a footswitch (not explicitly shown).

A block diagram of an impedance-matching electrosurgical system 100 inaccordance with the present disclosure will now be described withreference to FIG. 2. The impedance-matching electrosurgical system 100includes an electrosurgical RF generator 110 configured to selectivelyprovide electrosurgical energy. In embodiments, electrosurgical RFgenerator 110 is configured to output an RF signal in a frequency rangeof about 915 mHz to 925 mHz. It is to be understood, however, that a RFsignal encompassing an additional or alternative frequency or frequencyrange is envisioned within the scope of the present disclosure. The RFoutput of electrosurgical RF generator 110 is in electricalcommunication with RF measurement module 120 that is configured to sensea characteristic of the electrosurgical signal. For example withoutlimitation, RF measurement module 120 may be configured to sense theimpedance, reflectance, SWR, voltage, current, and/or power of theelectrosurgical signal. In embodiments, RF measurement module 120 mayinclude an integrated circuit, such as without limitation, an AnalogDevices AD8302 RF/IF Gain and Phase Detector.

Impedance-matching electrosurgical system 100 includes a controller 130that is in operable communication with RF measurement module 120, RFgenerator 110, PIN diode switching array 160, and user interface module140. Impedance-matching electrosurgical system 100 may be embodied inany of hardware, software, software in execution, firmware, microcode,bytecode, in virtualization, in a hardware description language, logicgates, circuitry, digital circuitry, RAM, ROM, MEMS, and the like. Userinterface 140 receives user input and provides the user input tocontroller 130. Controller 130 interprets the user input and controlsoperation of electrosurgical generation 110 in accordance therewith.

More particularly, controller 130 is configured to control RF generator110 and PIN diode switching array 160. In particular, RF generator 110generates sinusoidal waveforms of electrosurgical energy. RF generator110 can generate a plurality of waveforms having various duty cycles,peak voltages, crest factors and other suitable parameters. Certaintypes of waveforms are suitable for specific electrosurgical modes. Forinstance, RF generator 110 generates a 100% duty cycle sinusoidalwaveform in cut mode, which is best suited for ablating, fusing anddissecting tissue, and a 1-25% duty cycle waveform in coagulation mode,which is best used for cauterizing tissue to stop bleeding.

Controller 130 may include a microprocessor (not explicitly shown)operably connected to a memory (not explicitly shown) which may bevolatile type memory (e.g., RAM) and/or non-volatile type memory (e.g.,flash media, disk media, etc.). Controller 130 includes an output portthat is operably connected to RF generator 110 that allows controller130 to control the output of RF generator 110 according to either openand/or closed control loop schemes, and/or user input. Controller 130may include any suitable logic processor (e.g., control circuit),hardware, software, firmware, or any other logic control adapted toperform the features discussed herein.

Impedance-matching electrosurgical system 100 includes an RF measurementmodule 120, and also includes an interface to at least one sensor (notexplicitly shown) that is configured to measure a variety of tissue andenergy properties (e.g., tissue impedance, output current and/orvoltage, etc.) and to provide feedback to controller 130 in accordancewith the measured properties.

RF measurement module 120 is operative communication with controller130. The communication may be continuous or intermittent. The data maybe communicated in analog form, digital form, using a pulse widthmodulated signal, using a frequency or analog modulated signal, or anyother communication technology. Controller 130 is programmed to at leastprocess data to control the generation and impedance matching of theelectrosurgical energy.

Electrosurgical instrument 15 has one or more active electrodes 16 fortreating tissue T of patient P. As described herein, electrosurgicalinstrument 15 may be any type of electrosurgical instrument (e.g.,monopolar or bipolar) and may include active electrodes designed for awide variety of electrosurgical procedures (e.g., electrosurgicalcutting, ablation, etc.). Electrosurgical energy is supplied toelectrosurgical instrument 15 by impedance-matching electrosurgicalsystem 100 via transmission line 12, which is connected to an activeoutput terminal, allowing electrosurgical instrument 15 to coagulate,ablate, and/or otherwise treat tissue endogenically. Whenimpedance-matching electrosurgical system 100 is operated in a bipolarmode, the electrosurgical energy is returned to impedance-matchingelectrosurgical system 100 through a return pad 22 via cable 13 afterpassing through patient P.

The user interface 140 may include input controls, such as withoutlimitation, buttons, activators, switches, touch screen, and the like(not explicitly shown) for controlling impedance-matchingelectrosurgical system 100. Input controls may be include a handswitchdisposed on the instrument 15, a footswitch (not explicitly shown), or acontrol provided on the impedance-matching electrosurgical generator 10(i.e., a “front-panel” control). Additionally or alternatively, userinterface 140 may include one or more visual indicators and/or displayscreens (not explicitly shown) for providing the user with variety ofoutput information (e.g., intensity settings, treatment completeindicators, etc.). The user interface 140 allows the user (e.g., asurgeon, nurse, or technician) to adjust the electrosurgical energyparameters (e.g., power, waveform, duty cycle, voltage, current,frequency, and/or other parameters) to achieve the desiredelectrosurgical energy characteristics suitable for a particular task(e.g., coagulating, tissue sealing, intensity setting, etc.).Additionally or alternatively, user interface 140 may include a settabledesired tissue effect (e.g., hemostasis, coagulation, ablation,dissection, cutting, and/or to sealing tissue). The electrosurgicalinstrument 15 may also include one or more input controls (notexplicitly shown) that may be redundant with user interface 140 ofelectrosurgical generator 10.

Impedance-matching electrosurgical system 100 includes an impedancematching module 200 that includes a dynamic impedance matching network150 and a PIN diode switching array 160. As shown in FIG. 3, impedancematching module 200 includes an input 210, an output 211, a fixedreactive shunt section 201, a variable reactive series section 202, anda variable reactive shunt section 203. Reactive sections 201, 202, and203 are arranged in a pi configuration. Input isolation capacitor 205and output isolation capacitor 206 are coupled in series with input 210and output 211, respectively, to block DC current flow into or out ofthe RF signal path. In embodiments, input isolation capacitor 205 andoutput isolation capacitor 206 may have a value of about 1 nF.

In embodiments, fixed reactive shunt section 201 may include a fixedreactive element 230, which may be a capacitor, an inductor, or acombination thereof. Variable reactive series section 202 includes aplurality of reactive legs 231, 232, 233, 234 coupled in parallel, eachreactive leg 231, 232, 233, 234 having a PIN diode coupled in serieswith a reactive element, i.e., PIN diodes 244, 245, 246, 247 are coupledin series with reactive elements 240, 241, 242, and 243, respectively.The common junction 235, 236, 237, 237 of each PIN diode 244, 245, 246,and reactive element 240, 241, 242, and 243 are operably coupled to PINdiode control module 220. PIN diode control module is configured toselectively bias any of PIN diodes 244, 245, 246, 247 in accordance witha control signal received at control input 212.

Variable reactive shunt section 203 includes a plurality of reactivelegs 261, 262 coupled in parallel, each reactive leg 261, 262 having aPIN diode coupled in series with a reactive element, i.e., PIN diodes252, 253 are coupled in series with reactive elements 250, 251,respectively. A common junction 263, 264 of each PIN diode 252, 253 andreactive element 250, 251 are operably coupled to PIN diode controlmodule 220 that is configured to selectively bias any of PIN diodes 252,253 in accordance with a control signal received at control input 212.

Under forward bias, a PIN diode (i.e., PIN diodes 244, 245, 246, 247,252, 253) acts as a low resistance (short circuit) path that causes thecorresponding reactive element 235, 236, 237, 237, 250, 251 to beswitched in-circuit (i.e. activated). Conversely, under reverse bias, aPIN diode (i.e., PIN diodes 244, 245, 246, 247, 252, 253) acts as a highimpedance (open circuit) path that causes the corresponding reactiveelement 235, 236, 237, 237, 250, 251 to be switched out of the circuit(i.e. deactivated).

DC bias source 221 provides bias current to PIN diode control module 220that is configured to selectively apply bias to a PIN diode (i.e., PINdiodes 244, 245, 246, 247, 252, 253) as previously described. DC biassource 221 is isolated from the RF signal path by isolation inductors222, 223. Isolation capacitors 205, 206 also provide DC isolation aspreviously described herein. PIN diode control module may include anintegrated circuit, such as an Impellimax Decoded Five Channel −100V PINDiode Driver or a Supertex HV3922 PIN Diode Driver −220V.

In embodiments, the values of the reactance elements 235, 236, 237, 237,250, 251 are selected in accordance with binary encoding. For examplewithout limitation, an embodiment in accordance with the presentdisclosure may include reactive legs 231, 232, 233, 234 having animpedance (Z) corresponding to 5Ω, 10Ω, 20Ω, and 40Ω, respectively. Inthis manner, the reactive series section 202 is configured to providesixteen discrete values of reactance, i.e., from zero to 75Ω in 5Ωincrements. Variable reactive shunt section 203 includes reactive legs261, 262 that are configured to provide four discrete values. Forexample without limitation, reactive legs 261, 262 may have an impedance(Z) corresponding to 375Ω and 750Ω, respectively. In embodiments,controller 130 includes a look-up table for determining which reactiveelements to activate to achieve the required impedance correction.

The inventors have discovered relationships between reflectioncoefficient and impedance load which is best illustrated with referenceto the Smith diagram 400 of FIG. 4. In particular, reflectioncoefficients of two exemplary electrosurgical antenna types arediagrammed against load impedance varied over a range of less thannominal generator impedance (i.e., less than about 50Ω) to greater thannominal generator impedance (i.e., greater than about 50Ω). For example,the reflection coefficient of a surgical antenna is shown by plots 430and 440. The reflection coefficient of a percutaneous antenna is shownby plots 410 and 420. The plots reveal that the measured impedancemismatches, as plotted by the reflection coefficient data presentedtherein, are distributed in relatively narrow “bands.” The requiredimpedance matching range, i.e., tuning range of a dynamic impedancematching network, is thus greatly reduced. Correcting the impedancemismatch such that a corrected reflection coefficient is in a range ofabout zero to less than about 0.10, or in a range of about zero to lessthan about 0.15, yields a power transfer efficiency of greater thanabout 96%. A power transfer efficiency of greater than about 96% isconsidered to be within the acceptable operating range for anelectrosurgical system.

With reference now to FIG. 5A, a circular corrective region 450 enclosesthe set of data points representing reflection coefficients fallingwithin about less than 0.15 of the nominal, i.e., center point, ofcircular corrective region 450. In accordance with the presentdisclosure, the location and diameter of circular corrective region 450is determined by the corresponding values of reactive elements 201, 202,and 203. That is, the position and diameter of circular correctiveregion 450 is determined by the value of fixed reactance element 230,the aggregate value of reactive legs 231, 232, 233, and 234 of variablereactive series section 202, and the aggregate value of reactive legs261 and 262 of variable reactive shunt section 203. As previouslydescribed, in embodiments of the presently disclosed system, sixty-fouroverlapping reactance ranges are available to dynamically impedancematch the antenna to tissue. These overlapping ranges correspond to aseries of overlapping circular corrective regions 450-495 as exemplifiedin FIGS. 5A-5J. The diameter and position of circular corrective regions450-495 is dependent upon the selected aggregate reactance of thedynamic impedance matching network as described herein.

In an aspect of the present disclosure, a method of matching impedanceincludes the steps of measuring the impedance, identifying a correctiveregion in which the measured impedance falls, determining a combinationof reactive elements corresponding to the identified corrective region,and activating the combination of reactive elements to match themeasured impedance.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1. A method for performing impedance matching during an electrosurgicalprocedure, comprising the steps of: measuring an impedance; identifyinga corrective region in which the measured impedance falls; determining acombination of reactive elements corresponding to the identifiedcorrective region; and activating the combination of reactive elementsin accordance with the measured impedance.
 2. The method according toclaim 1, wherein the corrective region corresponds to a correctedreflection coefficient in a range of about zero to less than about 0.15.3. The method according to claim 1, wherein the corrective regioncorresponds to a corrected reflection coefficient in a range of aboutzero to less than about 0.10.
 4. The method according to claim 1,wherein the corrective region corresponds to a corrected power transferefficiency of greater than about 96%.
 5. The method according to claim1, further comprising the step of providing an impedance-matchingnetwork having selectively-activatable reactive elements arranged in api configuration having a first shunt reactive leg comprising a fixedreactance, a series reactive leg comprising a variable reactance, and asecond shunt reactive leg comprising a variable reactance.
 6. The methodaccording to claim 5, wherein the values of at least two of the reactiveelements are selected in accordance with binary encoding.
 7. The methodaccording to claim 1, wherein the determining step is performed inaccordance with binary encoding.
 8. The method according to claim 1,further comprising the step of providing at least one switching elementselected from the group consisting of a PIN diode, a field-effecttransistor, and a micromechanical switch, wherein the said at least oneswitching element configured to activate a said reactive element.
 9. Amethod for performing impedance matching during an electrosurgicalprocedure, comprising the steps of: providing an electrosurgicalgenerator in operable communication by transmission line to anelectrosurgical instrument, wherein the electrosurgical generatorincludes a plurality of selectively-activatable reactive elementsoperably associated with the transmission line; activating theelectrosurgical generator to apply electrosurgical energy to tissue;measuring an impedance relating to the transmission line; identifying acorrective region in which the measured impedance falls; determining acombination of reactive elements corresponding to the identifiedcorrective region; and activating the determined combination of reactiveelements.
 10. The method in accordance with claim 9, whereinselectively-activatable reactive elements are arranged in a piconfiguration having a first shunt reactive leg comprising a fixedreactance, a series reactive leg comprising a variable reactance, and asecond shunt reactive leg comprising a variable reactance.
 11. Themethod in accordance with claim 10, wherein a variable reactance legfurther includes a plurality of selectively activatable reactanceelements.
 12. The method in accordance with claim 11, wherein the valuesof the selectively activatable reactance elements are arranged inaccordance with binary encoding.
 13. The method in accordance with claim9, wherein the determining step is performed at least in part byreferencing a look-up table.
 14. The method according to claim 9,wherein the corrective region corresponds to a corrected reflectioncoefficient in a range of about zero to less than about 0.15.
 15. Themethod according to claim 9, wherein the corrective region correspondsto a corrected reflection coefficient in a range of about zero to lessthan about 0.10.
 16. The method according to claim 9, wherein thecorrective region corresponds to a corrected power transfer efficiencyof greater than about 96%.
 17. The method according to claim 9, whereinthe transmission line has a nominal impedance of about 50 ohms.
 18. Themethod according to claim 9, wherein the activation of a reactiveelement is performed at least in part by selectively biasing a PIN diodeassociated therewith.
 19. The method according to claim 9, wherein theactivation of a reactive element is performed at least in part byselectively activating a field-effect transistor associated therewith.20. The method according to claim 9, wherein the activation of areactive element is performed at least in part by selectively activatinga micromechanical switch associated therewith.